As you near Neil's shack, a super mutant named Neil approaches you and automatically starts a dialogue. He will tell you that a super mutant named Tabitha has taken over Black Mountain. One of her rules is that no humans are welcome to the area and any that approach should be shot on sight. This will automatically start the quest, which requires you to enter Tabitha's stronghold and put an end to her chaos.

To get you started, he will also let you know that the area is patrolled by super mutants during the day, while at night cloaked nightkin patrol the roads. With a Speech check of 50, you can convince Neil to assist you in killing Tabitha.
From Neil's shack you will have to make your way up the road towards Black Mountain. There is a long way where you will fight against three patrols and checkpoints of super mutants or nightkin. If you choose to take the normal path up the road, the 3rd Patrol of super mutants will include one nightkin. There are also two short cuts:

Short cut #1 (NE): On your way up you will find the body of an NCR trooper. If you pay close attention you will see a bear trap exactly at the legs of the corpse and all the way up to that hill. Be careful to avoid bear traps and falling rocks if you choose to take this path. You get a warning rock fall about half way up the path. A little beyond that point a trap is triggered and a giant Indiana Jones type boulder rolls down the path, which you can avoid by backing down the path until it flares out to the right or left and hugging the rocks to the side.

Short cut #2 (SE): This is the same as the short cut from Hidden Valley for the Still in the Dark quest. At the northeast end of the switchback path up the mountain, you'll see a rocky path going west. Follow that path to the irradiated crater with centaurs and the dead paladin patrol from the Brotherhood of Steel. Kill or sneak past them and climb the ridge to the south. This leads to the locked (75 Lockpick) gate into the Black Mountain compound, bypassing the Neil and nightkin encounter in the "village".

Be aware that a deathclaw may be waiting at the top of the summit (It has also been seen walking up the winding road to the summit of the mountain).
Once you reach the summit you have 3 options:

Talk to Neil and he will help you by misleading the guards at the entrance of the main buildings. This requires you and your companions to move past the guards by stealth since you choose to avoid fighting with them. When Neil returns from giving false information about "an intruder in the entrance of the Black Mountain" he will start walking back towards his previous location BUT he will not be alone: a number of cloaked nightkin will be directly behind him and at his side to check out the entrance of the area. Note that if you choose to bypass Neil and kill the nightkin at the summit by yourself, talking to him later will have no effect, since there is no one for him to fool; he will simply say, "OK. But whatever you have to do, be quick about it."

Use a ham radio which is located under the toppled satellite dish just across from Neil's position. You have 3 dialogue options:

Saying you are a big fan of the super mutants will send the remaining super mutants in the area towards your location.

The second option, which requires a speech check of 75 points (patch 1.01+), will cause Tabitha to say that she sentences the "Dumb-Dumbs" (non-nightkin super mutants) to death. It is also possible to pass this check with Speech 40, but for that you must know that Tabitha is paranoid, but since the flag is not set anywhere, this topic never appears (it seems that you were supposed to learn either from Neil or from Tabitha's radio broadcasts about Tabitha's paranoia, it may be cut content or a bug). Fighting will then break out between the super mutants and nightkin. The super mutants usually win the opening fight and are then attacked by more nightkin.

The third option will do nothing and is there only for those who change their mind.

If you have the means, you can of course just kill all the super mutants in the area.

At this point, you can choose to complete the quest one of two ways.

Enter the storage shed at the top of the mountain, where you will find a robot named Rhonda. If you decide to repair Rhonda, which requires a Science Skill of 60 points, you will receive the good ending of this quest: as you leave from the storage shed, Tabitha will appear, happy to see her robot repaired and fully functional again. She will not attack you (remaining friendly unless you attack), and you will instantly finish the quest with good Karma.

After doing this, you can still kill Tabitha and Rhonda and loot their corpses with no Karma penalty. You can also free Raul without Tabitha going hostile.

Enter the broadcast building instead and simply kill Tabitha. This carries no Karma penalty.

If you have a Science Skill of 25, you can hack Tabitha's personal computer (it doesn't have a special name, being simply labeled terminal). The last entry in this terminal says that Tabitha hides a second key to her personal room (where you can find her) below the stairs leading to her room.

Just after the radioactive crater, there's a domelike structure with several trunks, two of which contain several hundred caps. There is also a transceiver where you can pass a 75 speech check to get Tabitha to declare death to all 'Dumb-Dumbs'. The transceiver stops working after that.

With a low enough intelligence, a dialogue choice labeled "[Dumb] What?" will appear. After choosing this option, Tabitha will dismiss the player as a "Dumb-Dumb," and cut off the conversation.

After your party passes certain line, but not yet to Neil's place in the village, two groups of Super Mutant will spawn down the road, way back.

After completing this quest peacefully, Rhonda and Tabitha will make their way down the mountain to Neil's shack, where they will disappear from the game, but they will move very slowly; if they still remain in the Black Mountain, you need to be very careful, if you want to complete the Brotherhood of Steel quest peacefully, you have to be stealthy.

Although Rhonda and Tabitha will be friendly towards the player if the quest is completed peacefully, they are still allied with the super mutants, nightkin, and centaurs around Black Mountain, who become neutral upon completion. Attacking or killing any Black Mountain inhabitants, even in self-defense, will turn both Tabitha and Rhonda hostile.

If one or both of your companions are solely responsible for the kill, Tabitha and Rhonda may only become hostile to your companions and not you.

Freeing Raul first even without hiring him as a companion will cause Tabitha as well as Rhonda to immediately become hostile to the player.

However, if you have a high enough sneak skill, you can free Raul and sneak quickly to the storage building to repair Rhonda, causing Tabitha to initiate dialog when you exit the building and become friendly to you.

This quest can be completed without the involvement of Neil. Make your way through the super mutants and nightkin to the storage shed and repair Rhonda. The quest is not marked as started, however when you exit the storage shed you still have a 'good' ending with marking this quest completed.

Following the completion of the quest, super mutants and nightkin will still spawn in the area. They will be friendly but the player cannot interact with them.

ED-E is beneficial for this quest because of its perk allowing you to target the cloaked nightkin in V.A.T.S.

If Lily is your companion during/at the end of the quest, regardless of how you did it, she will say "Naughty Tabitha, Leo knows what you have done" or, "Tabitha! You naughty, naughty girl. Leo remembers what you did."

If Boone is your companion, he will attack Tabitha on sight when you reach her, rendering the good Karma ending unattainable. In PS3 version, if you have Boone wait outside the storage shed when repairing Rhonda, Dialogue will initialize immediately after you subsequently exit the shed (with Tabitha 'following' you), resulting in the good ending. in fact she will walk right past Boone on the way down the mountain and he will do nothing.

Occasionally, a few Boomers will be walking down the road from the summit.

ps3 Sometimes your companions will disappear while heading up black mountain. They will appear on your map but will not be there. For replication purposes I had ED-E and Boone with me. Saving your game (recommended to a new slot) then loading that game seems to fix this. [verified]

pcps3xbox360 Neil the super mutant will tell you to meet him at the top of the hill. He will be located to your left directly after you pass the crater (radiation warning). Talk to him when you see him and DO NOT go running ahead. If you go past him and start killing the nightkin, it is possible for a glitch to occur where Neil will not be able to join you regardless of the speech options and will always reply "OK. But whatever you have to do, be quick about it." If this happens, you can still complete the quest. This may still happen if you kill the Night Kin prior to even starting the quest. [verified]

ps3xbox360 If you accept Neil's help but enter Black Mountain itself from the locked gate on the southwest side (by Tabitha's room) instead of going through the checkpoints, Neil will run around randomly when you approach him and cannot be spoken to. Waiting causes his map marker to move near the domes, but he is nowhere to be found. [verified]

pcps3 The quest can be completed (but without the XP that should be gained and will appear as a new quest then a completed quest in your Pip-Boy the moment the quest is completed) by not visiting Neil's shack prior to exploring Black Mountain. Once Black Mountain is clear of all Mutants and Tabitha is dead, Neil will turn up thanking you for your help... even though you've never met him before! [verified]

xbox360 Repairing Rhonda to reunite with Tabitha before ever going to Neil's shack completes what would be the requirements for Crazy, Crazy, Crazy, however the quest is not added. You can then meet Neil for the first time at his shack and he will thank you. However the quest will still not appear as started or completed. [verified]

ps3xbox360pc If you wish to peacefully resolve the situation with Tabitha, ensure that you do not let a significant amount of in-game time pass between the moment when you first encounter Rhonda and the moment when you decide to repair her. It is highly likely that Rhonda will disappear from your game if you leave her room and decide to come back at a much later time. This can be fixed if you are playing the PC version with access to the console by using the command player.placeleveledactoratme 000E84A2. Please note that achievements will be disabled until you have restarted the game-client, so it would be advised to save before and immediately after using the command, then exit the game-client completely and load it up again. Also note that by using this command, you will circumvent the science check. [verified]

xbox360pc If you restore Rhonda and spend too much time in the Storage House, Tabitha may enter as a hostile - if you kill her, you will finish the quest but may be locked inside of the Storage House. Sometimes the door will unlock after killing Rhonda, after you kill Tabitha. [verified]

pc If you have completed the quest peacefully and it's bugged but Tabitha has already disappeared, open the console and type prid 000e61a2 to select Tabitha (shes invisible). Then type moveto player to move her to the player then type enable to cause her to respawn, press E on her and the quest should complete normally. Alternatively, you can simply type prid 000e61a2 then type kill to kill her and complete the quest the 'bad' way. [verified]

pcxbox360 Sometimes the dead NCR soldier near the bear traps is alive. [verified]

xbox360ps3 After repairing Rhonda and finishing the quest, Rhonda and Tabitha may suddenly disappear if you attempt to follow them. [verified]

ps3xbox360 While traveling up the mountain ED-E will sometimes disappear. [verified]

pc If you have completed the quest peacefully and return to Black Mountain some time afterward, the nightkin may be hostile and attack you on sight but the other super mutants are neutral and do not join the nightkin in attacking unless you attack them. [verified]

pcxbox360 If you save right after finishing the quest by the peaceful way, and then you load that game, Rhonda might break into pieces which remain static in the air. Nonetheless, she will continue walking alongside Tabitha. [verified]

pcxbox360 After convincing Neil to become a decoy he may be stuck behind a rock with him attempting to run towards the camp but not moving at all. This is then followed by the Nightkins running down the road despite being given no notice of any intruder. [verified]